Most human infants produce ample quantities of lactase for milk digestion. However, in the vast majority of adult humans, the
gene which specifies production of lactase is turned "off" and these individuals cannot digest lactose - they are lactose
intolerant.

Even with our eyes closed, we have a sense of body position - where our arms and legs are, for example, and that we are moving
them. Muscles, tendons, joints and the inner ear contain proprioceptors, also known as stretch receptors, which relay
positional information to our brains.

Receptors on our tongues bind to chemicals in our food and relay the information about the chemicals to our brain.
Surprisingly, all those wonderful tastes are transmitted to our brains through only four types of receptors on our tongues -
those for sweet, sour, salt and bitter.